The usual method of providing a uniformly illuminated source of diffuser light is to place a condensing lens between a point light source and a diffusing screen. The condensing lens has to be a certain distance from the diffusing screen and the light bulb to work properly. If the light level at the diffusing screen is to be varied, it is necessary to use neutral density filters, a variable iris or a combination of the two. The resulting structure requires a great deal of space, is difficult to fabricate and is very expensive.